Umbrella base



FIG. 1 is a perspective view of an umbrella base showing a new design;

FIG. 2 is another perspective view of the design of FIG. 1;

FIG. 3 is a top view of the design of FIG. 1;

FIG. 4 is a rear view of the design of FIG. 1;

FIG. 5 is a front view of the design of FIG. 1;

FIG. 6 is a left side view of the design of FIG. 1; and,

FIG. 7 is a right side view of the design of FIG. 1. The dot-dash line represents a boundary of the claimed design. The evenly broken lines depict portions of the umbrella base that form no part of the claimed design. 

CLAIM The ornamental design for an umbrella base, as shown and described. 